As a device which detects capacitances of capacitors arranged in a matrix pattern, Cited Document 1 discloses a capacitance detecting circuit which detects distribution of capacitances of a capacitor matrix in which capacitors are formed between M drive lines and L sense lines. The capacitance detecting circuit, which utilizes the fact that a capacitance of a capacitor located at a touched position becomes small when a finger or a pen touches a touch panel, detects, by detecting a change in capacitance, a position touched by a finger or a pen on the touch panel.
FIG. 13 is a view schematically illustrating a configuration of a conventional touch panel system 900. FIG. 14 is a view for explaining how the touch panel system 900 is driven. The touch panel system 900 includes a touch panel 902 and a touch panel controller 903. The touch panel 902 has (i) drive lines DL1 through DL4, (ii) sense lines SL1 through SL4, and (iii) capacitors C11 through C44 arranged at respective intersections of the drive lines DL1 through DL4 and the sense lines SL1 to SL4. The touch panel controller 903 includes a driving section 904 and amplifiers 908.
The following description will discuss how the touch panel system 900 converts a capacitance into a measured value (detected value).
The driving section 904 drives the drive lines DL1 through DL4 in accordance with a code sequence, having four columns and four rows, expressed by Expression 3 shown in FIG. 14. In a case where an element of the code sequence is “1 (one)”, the driving section 904 applies a power-supply voltages VDD to the drive lines DL1 through DL4. In a case where an element of the code sequence is “0 (zero)” the driving section 904 applies no voltage to the drive lines DL1 through DL4.
The touch panel system 900 has four amplifiers 908 arranged so as to correspond to the respective sense lines SL1 to SL4. Each of the amplifiers 908 receives and amplifies linear sums Y1 through Y4 of the capacitors along a corresponding one of the sense lines SL1 through SL4 driven by the driving section 904.
Specifically, out of four times of driving in accordance with the code sequence having four columns and four rows, the driving section 904 applies, during the first time of driving, a power-supply voltage VDD to the drive line DL1, while applying no voltage to the rest drive lines DL2 through DL4. This causes an output corresponding to the capacitor C31, which output is expressed by Expression 1 shown in FIG. 14, to be supplied from, for example, the sense line SL3 to a corresponding one of the amplifiers 908 as a measured value Y1.
During the second time of driving, the driving section 904 applies a power-source voltage VDD to the drive line DL2, while applying no voltage to the rest drive lines DL1, DL3, and DL4. This causes an output corresponding to the capacitor C32, which output is expressed by Expression 2 shown in FIG. 14, to be supplied from the sense line SL3 to the corresponding one of the amplifiers 908 as a measured value Y2.
Similarly, during the third time of driving, the driving section 904 applies a power-source voltage VDD to the drive line DL3, while applying no voltage to the rest drive lines DL1, DL2, and DL4. Thereafter, during the fourth time of driving, the section 904 applies a power-source voltage VDD to the drive line DL4, while applying no voltage to the rest drive lines DL1 through DL3. By the third and the fourth times of driving, measured values Y3 and Y4 corresponding to the capacitors C3 and C4, respectively, are obtained.
In this manner, the measured values Y1, Y2, Y3, and Y4 are associated with capacitances C1, C2, C3, and C4, respectively (see Expressions 3 and 4 shown in FIG. 14).